This invention relates to novel polyimides, novel polyamic acids which are intermediates thereof, a process for producing the same and novel acid dianhydrides to be used in the production of these novel polyimides. More particularly, it relates to novel polyimides obtained by introducing a monomer unit derived from acid dianhydrides substituted by a substituent having an alkyl or fluoroalkyl group into the molecule and these acid dianhydrides.
Because of being excellent in heat resistance among various organic polymers, polyimides have been widely used in the fields of, for example, cosmology, aeronautics, electronic communication and office automation instruments. In recent years, there have been particularly required polyimides which have not only a high heat resistance but also various functions appropriate for uses.
In general, a polyimide has a relatively high water absorption due to the large polarization between Cxe2x95x90O and N in its imide ring. To improve the existing polyimides, it is therefore one of the problems to be solved to reduce the water absorption.
As one of methods for reducing the water absorption of polyimides, JP-A-57-143329, JP-A-61-57620, JP-A-2-225522, JP-A-4-7333 and JP-A-4-100020 disclose a method of introducing alkyl and fluoroalkyl groups (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d). In this method, diamines having an alkyl or fluoroalkyl group is used to thereby introduce these substituents into polyimides. However, there has been reported so far no polyimide obtained by introducing an alkyl or fluoroalkyl group into an acid dianhydride and then reacting it with a diamine. This is seemingly because there is known no acid dianhydride having an alkyl or fluoroalkyl group per se.
As the results of intensive studies, the present inventors have found out acid dianhydrides carrying a substituent having alkyl or fluoroalkyl group introduced thereinto and a process for producing novel polyimides by using the same. The invention has been completed based on these findings.
The polyimide according to the invention is a polyimide containing a structure represented by the following general formula (I): 
wherein
X1 represents a tetravalent organic group having a substituent xe2x80x94R1AR2 (wherein A represents a divalent linkage group; R1 represents a single bond or a C1-3 alkylene group; and R2 represents a C1-25 alkyl group or a fluoroalkyl group); and
Y represents a divalent organic group.
The term xe2x80x9corganic groupxe2x80x9d as used herein means a group which is a part of an organic compound and has linkage site(s) (the number of these linkage sites is expressed as valency). Aromatic groups and aliphatic groups may fall within the category of the organic group. It is preferable that the organic group has at least a part of its linkage sites on aromatic carbon atom(s). Although the organic group is not particularly restricted in bulkiness, it typically carries from 15 to 74, preferably from 19 to 59 and still preferably form 26 to 46, carbon atoms.
The term xe2x80x9clinkage groupxe2x80x9d as used herein means a divalent functional group which consists of, if necessary, hydrogen atom(s), carbon atom(s) and at least one heteroatom selected from among, for example, oxygen, nitrogen and sulfur atoms and has at least one of the linkage sites on the hetero atom.
In one embodiment of the invention, A is an ester bond, an amide bond or a sulfonamide bond. An ester bond is a group formed by dehydrating condensation of an oxo acid with an alcohol. For example, an ester bond of a carboxylic acid ester may be represented by xe2x80x94COOxe2x80x94 or xe2x80x94OCOxe2x80x94. The same applies to other oxo acid esters. An amide bond may be represented by xe2x80x94NHxe2x80x94COxe2x80x94 or xe2x80x94COxe2x80x94NHxe2x80x94. A sulfonamide bond may be represented by xe2x80x94NHxe2x80x94SO2xe2x80x94 or xe2x80x94SO2xe2x80x94NHxe2x80x94.
In one embodiment of the invention, the polyimide is a copolymer having a structure represented by the following general formula (II): 
wherein
X1 represents a tetravalent organic group having a substituent xe2x80x94R1AR2 (wherein A represents a divalent linkage group; R1 represents a single bond or a C1-3 alkylene group; and R2 represents a C1-25 alkyl group or a fluoroalkyl group);
X2 is a tetravalent organic group different from X1;
Y represents a divalent organic group;
m is an integer of 1 or more;
n is an integer of 0 or more; and
m/m+n is 0.01 or more; and
having an average molecular weight of from 5,000 to 1,000,000.
m and n represent respectively the numbers of imide units contained in the copolymer molecule, while m/m+n represents the ratio of the imide unit having X1. m preferably ranges from 1 to 100, n preferably ranges 0 to 99 and m+n preferably ranges from 1 to 100. m/m+n preferably ranges from 0.01 to 1, still preferably form 0.1 to 1 and still preferably from 0.2 to 1.
X1, X2 and Y may each occur in plural types in a polymer molecule.
The term xe2x80x9caverage molecular weightxe2x80x9d as used herein means weight-average molecular weight measured by gel permeation chromatography (GPC). It preferably ranges from 3,000 to 1,000,000, still preferably from 10,000 to 500,000 and still preferably from 20,000 to 300,000.
In one embodiment of the invention, X1 is represented by the following general formula: 
wherein
Z represents a divalent aromatic or aliphatic group having a substituent xe2x80x94R1AR2 (wherein A represents a divalent linkage group; R1 represents a single bond or a C1-3 alkylene group; and R2 represents a C1-25 alkyl group or a fluoroalkyl group); and
L is xe2x80x94Oxe2x80x94 or xe2x80x94NHxe2x80x94.
The term xe2x80x9caromatic groupxe2x80x9d means a group containing at least one aromatic ring (for example, aryl, heteroaryl, arylalkyl). It carries typically from 15 to 74, preferably form 19 to 59 and still preferably from 26 to 46, carbon atoms in total.
The term xe2x80x9caliphatic groupxe2x80x9d means a group having an aliphatic moiety but being free from aromatic rings. It carries typically from 1 to 60, preferably form 5 to 45 and still preferably from 12 to 32, carbon atoms.
In one embodiment of the invention, Z is represented by one of the following general formulae: 
wherein R2 represents a C1-25 alkyl group or a fluoroalkyl group; and p is from 1 to 4.
The above general formulae representing Z all indicate that Z can link at any two sites on the aromatic ring. It is preferable that p is from 1 to 3.
In one embodiment of the invention, Z is xe2x80x94CH2CH(COOR2)CH(COOR2)CH2xe2x80x94, xe2x80x94CH2CH(OCOR2)CH(OCOR2)CH2xe2x80x94, xe2x80x94CH2C(CH2COOR2)2CH2xe2x80x94, xe2x80x94CH2C(CH2OCOR2)2CH2xe2x80x94, xe2x80x94CH(CH2COOR2)CH(CH2COOR2)xe2x80x94, xe2x80x94CH(CH2COOR2)CH(CH2OCOR2)xe2x80x94 or xe2x80x94CH2CH(CH2COOR2)xe2x80x94,
wherein R2 represents a C1-25 alkyl group or a fluoroalkyl group.
The polyimide composition of the invention is a composition containing one of the polyimides as described above. This composition may contain an arbitrary liquid or powder as a diluting medium wherein the polyimide can be dissolved or uniformly dispersed.
The polyamic acid according to the invention contains a structure represented by the following general formula (III): 
wherein
X1 represents a tetravalent organic group having a substituent xe2x80x94R1AR2 (wherein A represents a divalent linkage group; R1 represents a single bond or a C1-3 alkylene group; and R2 represents a C1-25 alkyl group or a fluoroalkyl group); and
Y represents a divalent organic group.
In one embodiment of the invention, A is an ester bond, an amide bond or a sulfonamide bond.
In one embodiment of the invention, the polyamic acid is a copolymer having a structure represented by the following general formula (IV) or a structure represented by the following general formula (IV) wherein some of the amic acid moiety has been dehydrated and condensed: 
wherein
X1 represents a tetravalent organic group having a substituent xe2x80x94R1AR2 (wherein A represents a divalent linkage group; R1 represents a single bond or a C1-3 alkylene group; and R2 represents a C1-25 alkyl group or a fluoroalkyl group);
X2 is a tetravalent organic group different from X1;
Y represents a divalent organic group;
m is an integer of 1 or more;
n is an integer of 0 or more; and
m/m+n is 0.01 or more; and
having an average molecular weight of from 5,000 to 1,000,000.
In one embodiment of the invention, X1 is represented by the following general formula: 
wherein
Z represents a divalent aromatic or aliphatic group having a substituent xe2x80x94R1AR2 (wherein A represents a divalent linkage group; R1 represents a single bond or a C1-3 alkylene group; and R2 represents a C1-25 alkyl group or a fluoroalkyl group) and
L is xe2x80x94Oxe2x80x94 or xe2x80x94NHxe2x80x94.
In one embodiment of the invention, Z is represented by one of the following general formulae: 
wherein R2 represents a C1-25 alkyl group or a fluoroalkyl group; and p is from 1 to 4.
In one embodiment of the invention, Z is xe2x80x94CH2CH(COOR2)CH(COOR2)CH2xe2x80x94, xe2x80x94CH2CH(OCOR2)CH(OCOR2)CH2xe2x80x94, xe2x80x94CH2C(CH2COOR2)2CH2xe2x80x94, xe2x80x94CH2C(CH2OCOR2)2CH2xe2x80x94, xe2x80x94CH(CH2COOR2)CH(CH2COOR2)xe2x80x94, xe2x80x94CH(CH2COOR2)CH(CH2OCOR2)xe2x80x94 or xe2x80x94CH2CH(CH2COOR2)xe2x80x94,
wherein R2 represents a C1-25 alkyl group or a fluoroalkyl group.
The acid dianhydride according to the invention has a structure represented by the following general formula (V): 
wherein
X1 represents, a tetravalent organic group having a substituent xe2x80x94R1AR2 (wherein A represents a divalent linkage group; R1 represents a single bond or a C1-3 alkylene group; and R2 represents a C1-25 alkyl group or a fluoroalkyl group).
In one embodiment of the invention, A is an ester bond, an amide bond or a sulfonamide bond.
In one embodiment of the invention, X1 is represented by the following general formula: 
wherein
Z represents a divalent aromatic or aliphatic group having a substituent xe2x80x94R1AR2 (wherein A represents a divalent linkage group; R1 represents a single bond or a C1-3 alkylene group; and R2 represents a C1-25 alkyl group or a fluoroalkyl group); and
L is xe2x80x94Oxe2x80x94 or xe2x80x94NHxe2x80x94.
In one embodiment of the invention, Z is represented by one of the following general formulae: 
wherein R2 represents a C1-25 alkyl group or a fluoroalkyl group; and p is from 1 to 4.
In one embodiment of the invention, Z is xe2x80x94CH2CH(COOR2)CH(COOR2)CH2xe2x80x94, xe2x80x94CH2CH(OCOR2)CH(OCOR2)CH2xe2x80x94, xe2x80x94CH2C(CH2COOR2)2CH2xe2x80x94, xe2x80x94CH2C(CH2OCOR2)2CH2xe2x80x94, xe2x80x94CH(CH2COOR2)CH(CH2COOR2)xe2x80x94, xe2x80x94CH(CH2COOR2)CH(CH2OCOR2)xe2x80x94 or xe2x80x94CH2CH(CH2COOR2)xe2x80x94,
wherein R2 represents a C1-25 alkyl group or a fluoroalkyl group.
The process according to the invention is a process for producing a polyimide involving the step of reacting an acid dianhydride with a diamine, wherein the polyimide contains a structure represented by the following general formula (I): 
wherein
X1 represents a tetravalent organic group having a substituent xe2x80x94R1AR2 (wherein A represents a divalent linkage group; R1 represents a single bond or a C1-3 alkylene group; and R2 represents a C1-25 alkyl group or a fluoroalkyl group); and
Y represents a divalent organic group.
The process according to the invention is a process for producing a polyamic acid involving the step of reacting an acid dianhydride with a diamine, wherein the polyamic acid contains a structure represented by the following general formula (III): 
wherein
X1 represents a tetravalent organic group having a substituent xe2x80x94R1AR2 (wherein A represents a divalent linkage group; R1 represents a single bond or a C1-3 alkylene group; and R2 represents a C1-25 alkyl group or a fluoroalkyl group); and
Y represents a divalent organic group.
The process according to the invention is a process for producing an acid dianhydride involving the step of reacting a dihydroxybenzene derivative or a diaminobenzene derivative with an alkylating agent and a trimellitic acid anhydride derivative, wherein the acid dianhydride has a structure represented by the following general formula (V): 
wherein
X1 is represented by the following general formula: 
wherein
Z represents a divalent aromatic or aliphatic group having a substituent xe2x80x94R1AR2 (wherein A represents a divalent linkage group; R1 represents a single bond or a C1-3 alkylene group; and R2 represents a C1-25 alkyl group or a fluoroalkyl group); and
L represents xe2x80x94Oxe2x80x94 or xe2x80x94NHxe2x80x94.
The gist of the invention relating to the novel polyimides resides in the acid dianhydrides substituted by a substituent having an alkyl or fluoroalkyl group and utilization thereof.
The novel polyimide according to the invention is a polyimide containing a structure represented by the following general formula (I): 
wherein
X1 represents a tetravalent organic group having a substituent xe2x80x94R1AR2 (wherein A represents a divalent linkage group; R1 represents a single bond or a C1-3 alkylene group; and R2 represents a C1-25 alkyl group or a fluoroalkyl group); and
Y represents a divalent organic group.
The novel polyamic acid according to the invention is a polyamic acid containing a structure represented by the following general formula (III): 
wherein
X1 represents a tetravalent organic group having a substituent xe2x80x94R1AR2 (wherein A represents a divalent linkage group; R1 represents a single bond or a C1-3 alkylene group; and R2 represents a C1-25 alkyl group or a fluoroalkyl group); and
Y represents a divalent organic group.
The novel acid dianhydride according to the invention is an acid dianhydride having a structure represented by the following general formula (V): 
wherein
X1 represents a tetravalent organic group having a substituent xe2x80x94R1AR2 (wherein A represents a divalent linkage group; R1 represents a single bond or a C1-3 alkylene group; and R2 represents a C1-25 alkyl group or a fluoroalkyl group).
Next, embodiments of the novel polyimide according to the invention will be described by reference to particular structural examples thereof. However, the polyimide is not particularly restricted in structure, so long as it is a polyimide composition having an alkyl or fluoroalkyl group in a side chain of an acid dianhydride residue.
Particular examples of the process for producing the polyimide according to the invention include: 1) a process wherein an acid dianhydride having an alkyl or fluoroalkyl group is preliminarily synthesized and then reacted with an arbitrary diamine to give a polyamic acid followed by cyclodehydration thereby giving a polyimide; and 2) a process wherein 1 equivalent of an arbitrary diamine is reacted with 2 equivalents of trimellitic acid anhydride chloride or with 2 equivalents of trimellitic acid anhydride in the presence of a condensing agent to give a dicarboxylic acid which is then reacted with a diamine having an alkyl or fluoroalkyl group thereby giving a polyimide.
First, illustration will be made on the process 1) wherein an acid dianhydride having an alkyl or fluoroalkyl group is preliminarily synthesized and then reacted with an arbitrary diamine to give a polyamic acid followed by cyclodehydration thereby giving a polyimide.
As the acid dianhydride to be used as the starting material of the novel polyimide of the general formula (I), use may be made of those represented by the following general formulae (2-1), (2-2) and (2-3): 
wherein R2 represents a C1-25 alkyl group or a fluoroalkyl group; and p is from 1 to 4.
As the acid dianhydride to be used as the starting material of the novel polyimide of the general formula (I), use may be also made of those represented by the following general formulae (2-4), (2-5), (2-6) and (2-7): 
wherein R2 represents a C1-25 alkyl group or a fluoroalkyl group; and p is from 1 to 4.
As the acid dianhydride to be used as the starting material of the novel polyimide of the general formula (I), use may be also made of those represented by the following general formula (2-8): 
wherein
Zxe2x80x2 is xe2x80x94CH2CH(COOR2)CH(COOR2)CH2xe2x80x94, xe2x80x94CH2CH(OCOR2)CH(OCOR2)CH2xe2x80x94, xe2x80x94CH2C(CH2COOR2)2CH2xe2x80x94, xe2x80x94CH2C(CH2OCOR2)2CH2xe2x80x94, xe2x80x94CH(CH2COOR2)CH(CH2COOR2)xe2x80x94 or xe2x80x94CH(CH2COOR2)CH(CH2OCOR2)xe2x80x94.
As the acid dianhydride to be used as the starting material of the novel polyimide of the general formula (I), use may be also made of those represented by the following general formula (2-9): 
wherein R2 represents a C1-25 alkyl group or a fluoroalkyl group; and p is from 1 to 4.
Now, R1 in the invention will be described. In case where the substituent xe2x80x94R1AR2 is attached to an aliphatic carbon atom, R1 is a single bond or an alkylene group, preferably a single bond or a methylene group. In case where the substituent xe2x80x94R1AR2 is attached to an aromatic carbon atom, R1 is always defined as a single bond.
Next, R2 in the invent ion (i.e., a C1-25 alkyl or fluoroalkyl group) will be described. A C1-25 alkyl group means a xe2x80x94ChH2h+1 group (wherein h is from 1 to 25), while a C1-25 fluoroalkyl group means a xe2x80x94CiHjFk group (wherein i is form 1 to 25 and j+k is 2i+1).
With respect to the carbon atom number of t he alkyl or fluoroalkyl group, a carbon atom number of a certain extent is needed to achieve a low water absorption. When the carbon atom number is too large, the acid dianhydride becomes hardly soluble in solvents which are used in synthesizing an amic acid serving as a precursor of the polyimide. In this case, the acid dianhydride becomes waxy and thus can be hardly handled. Thus, the carbon atom number available herein ranges from 1 to 25, preferably from 3 to 20 and still preferably from 5 to 18. Preferable examples of the alkyl group include C5-18 alkyl groups such as hexyl, heptyl, octyl, nonyl and decyl groups.
In case where R2 is a fluoroalkyl group xe2x80x94CiHjFk, k is 1 or more, j is 0 or more and j+k preferably ranges from 3 to 51, more preferably from 7 to 41 and most preferably from 11 to 37. Preferable examples of the fluoroalkyl group include xe2x80x94CH2CH2(CF2)4CF3 to xe2x80x94CH2CH2(CF2)14CF3 and xe2x80x94(CF2)2CF3 to xe2x80x94(CF2)16CF3 having 1 to 25, preferably 3 to 20 and still preferably 5 to 18, carbon atoms.
Now, particular examples of the process for producing a novel acid dianhydride will be described.
First, an example of the process for producing novel acid dianhydrides represented by the general formula (2-1) as shown above will be illustrated.
An alkali metal (Li, Na, K, Rb, Cs, Fr) salt of dihydroxybenzenecarboxylic acid is reacted with R2xe2x80x94Qxe2x80x2 (wherein Qxe2x80x2 represents a halogen other than fluorine) in an aprotic polar solvent under heating to give (HO)2xe2x80x94C6H3xe2x80x94COOR2. This product is reacted with 2 times by mol as much trimellitic acid anhydride chloride or with 2 times by mol as much trimellitic acid anhydride in the presence of a condensing agent to thereby give a novel acid dianhydride represented by the general formula (2-1). Compounds wherein p is from 2 to 4 can be obtained by substituting the dihydroxybenzenecarboxylic acid respectively by dihydroxybenzenedicarboxylic acid, dihydroxybenzenetricarboxylic acid and dihydroxybenzenetetracarboxylic acid.
Next, an example of the process for producing novel acid dianhydrides represented by the general formula (2-2) will be illustrated.
(HO)2xe2x80x94C6H3xe2x80x94NHCOR2 can be obtained by reacting dihydroxyaminobenzene with R2COCl or with R2OOH in the presence of a condensing agent. Then this product is reacted with 2 times by mol as much trimellitic acid anhydride chloride or with 2 times by mol as much trimellitic acid anhydride in the presence of a condensing agent to thereby give a novel acid dianhydride represented by the general formula (2-2). Compounds wherein p is from 2 to 4 can be obtained by substituting the dihydroxyaminobenzene respectively by dihydroxydiaminobenzene, dihydroxytriaminobenzene and dihydroxytetraaminobenzene.
Next, an example of the process for producing novel acid dianhydrides represented by the general formula (2-3) will be illustrated.
Compounds represented by the general formula (2-3) can be obtained as in the case of the compounds of the general formula (2-2) but substituting R2COCl by R2SO2Cl.
Next, an example of the process for producing novel acid dianhydrides represented by the general formula (2-4) will be illustrated.
Novel acid dianhydrides represented by the general formula (2-4) can be obtained by reacting diaminodihydroxybenzene with 2 times by mol as much trimellitic acid chloride and then with R2COCl. Compounds wherein p is from 2 to 4 can be obtained by using diaminodihydroxybenzene, diaminotrihydroxybenzene and diaminotetrahydroxybenzene.
Next, an example of the process for producing novel acid dianhydrides represented by the general formula (2-5) will be illustrated.
An alkali metal (Li, Na, K, Rb, Cs, Fr) salt of diaminobenzenecarboxylic acid is reacted with R2xe2x80x94Qxe2x80x2 (wherein Qxe2x80x2 represents a halogen other than fluorine) in an aprotic polar solvent under heating to give (H2N)2xe2x80x94C6H3xe2x80x94COOR2. This product is reacted with 2 times by mol as much trimellitic acid anhydride chloride or with 2 times by mol as much trimellitic acid anhydride in the presence of a condensing agent to thereby give a novel acid dianhydride represented by the general formula (2-5). Compounds wherein p is from 2 to 4 can be obtained by substituting the diaminobenzenecarboxylic acid respectively by diaminobenzenedicarboxylic acid, diaminobenzenetricarboxylic acid and diaminobenzenetetracarboxylic acid.
Next, an example of the process for producing novel acid dianhydrides represented by the general formula (2-6) will be illustrated.
Novel acid dianhydrides represented by the general formula (2-6) can be obtained by reacting diaminobenzyl alcohol with 2 times by mol as much trimellitic acid chloride and then with R2COCl. Compounds wherein p is from 2 to 4 can be obtained by substituting the diaminobenzyl alcohol respectively by (H2N)2C6H2(CH2OH)2, (H2N)2C6H(CH2OH)3 and (H2N)2C6(CH2OH)4.
Next, an example of the process for producing novel acid dianhydrides represented by the general formula (2-7) will be illustrated.
Compounds represented by the general formula (2-7) can be obtained as in the case of the compounds of the general formula (2-6) but substituting R2COCl by R2SO2Cl.
Next, an example of the process for producing novel acid dianhydrides represented by the general formula (2-8) will be illustrated.
HOCH2CH(OH)CH2xe2x80x94OCOR2 can be obtained by reacting HOCH2CH(OH)CH2xe2x80x94Q (wherein Q represents a halogen) with an alkali metal salt of R2COOH in an aprotic polar solvent under heating. This product is reacted with 2 times by mol as much trimellitic acid anhydride chloride or with 2 times by mol as much trimellitic acid anhydride in the presence of a condensing agent to thereby give a novel acid dianhydride represented by the general formula (2-8).
Next, an example of the process for producing novel acid dianhydrides represented by the general formula (2-9) will be illustrated.
(HOCH2)2C(CH2OCOR2)2 can be obtained by reacting, for example, (HOCH2)2C(CH2Q)2 (wherein Q represents a halogen) with an alkali metal salt of R2COOH in an aprotic polar solvent under heating. This product is reacted with 2 times by mol as much trimellitic acid anhydride chloride or with 2 times by mol as much trimellitic acid anhydride in the presence of a condensing agent to thereby give a novel acid dianhydride represented by the general formula (2-9). Acid dianhydrides having corresponding structures can be obtained by the same procedure but substituting (HOCH2)2C(CH2Q)2 by HOxe2x80x94CH2CHQCHQCH2xe2x80x94 OH or QCH2CH(OH)CH(OH)CH2Q.
Novel acid dianhydrides represented by the general formula (2-9) can be obtained by reacting an alkali metal salt of HOCH2CH(COOH)CH(COOH)CH2OH, HOCH2C(CH2COOH)2CH2OH or CH2(COOH)CH(OH)CH(OH)CH2(COOH) in an aprotic polar solvent under heating and then reacting this product with 2 times by mol as much trimellitic acid anhydride chloride or with 2 times by mol as much trimellitic acid anhydride in the presence of a condensing agent.
The acid dianhydrides represented by the general formulae (2-1) to (2-9) obtained by the reactions as described above are examples which are particularly useful as monomers of the novel polyimides. Other acid dianhydrides represented by the general formula (V) can be also obtained in accordance with one of these processes with the combined use of known starting compounds and reactions.
Next, a process for synthesizing a polyimide via a polyamic acid will be described by way of example.
A polyimide can be obtained by reacting a novel acid dianhydride represented by one of the general formulae (2-1) to (2-9) obtained above with a diamine in an organic polar solvent to give a polyamic acid and then thermally or chemically imidating the polyamic acid.
In this reaction, either a single acid dianhydride or a mixture of two or more acid dianhydrides may be used as the acid dianhydride. Similarly, either a single diamine or a mixture of two or more diamines may be used.
The term xe2x80x9cthermally imidatexe2x80x9d as used herein means a method wherein a polyamic acid is converted into a polyimide by merely heating.
The term xe2x80x9cchemically imidatexe2x80x9d as used herein means a method wherein a dehydrating agent in a stoichiometric amount or more and a basic catalyst are added to a polyamic acid polymer or its solution and then imidataion is carried out by heating.
The dehydrating agent as used herein is exemplified by aliphatic acid anhydrides (for example, acetic anhydride) and aromatic acid anhydrides. The basic catalyst is exemplified by aliphatic tertiary amines (for example, triethylamine), aromatic tertiary amines (for example, dimethylaniline) and heterocyclic tertiary amines (for example, pyridine, picoline, isoquinoline).
It is desirable that the polyamic acid has an average molecular weight of from 5,000 to 1,000,000. In case where it has an average molecular weight less than 5,000, the resultant polyimide has only a low molecular weight. It is undesirable to use this polyimide as such as a photoreactive resin, since there arises an undesirable problem that the resin becomes brittle. It is also undesirable that the average molecular weight of the polyamic acid exceeds 1,000,000, since there arises another problem in this case that the polyamic acid varnish becomes too viscous and shows poor handling properties.
Examples of the organic polar solvent to be used in the reaction of producing the polyamic acid include sulfoxide solvents (for example, dimethyl sulfoxide, diethyl sulfoxide), formamide solvents (for example, N,N-dimethylformamide, N,N-diethylformamide), acetamide solvents (for example, N,N-dimethylacetamide, N,N-diethylacetamide), pyrrolidone solvents (for example, N-methyl-2-pyrrolidone, N-vinyl-2-pyrrolidone), phenol solvents (for example, phenol, o-, m- or p-cresol, xylenol, halogenated phenols, catechol), hexamethylphosphoramide and xcex3-butyrolactone. Although it is desirable to use one of these solvents or a mixture thereof, it is also possible to use aromatic hydrocarbons (for example, xylene, toluene) as a part of the solvent.
To synthesize the polyimides having an alkyl or fluoroalkyl group according to the invention, use can be made of the acid dianhydrides represented by the general formulae (2-1) to (2-9) of the invention together with other acid dianhydrides, so long as the content of the acid dianhydrides represented by the general formulae (2-1) to (2-9) of the invention amounts to 1% or more of the total acid dianhydrides.
The other acid dianhydrides are not particularly restricted stricted so long as they are acid dianhydrides. For example, use may be made therefor of aliphatic or alicyclic tetracarboxylic acid dianhydrides (for example, butanetetracarboxylic acid dianhydride, 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride, 1,3-dimethyl-1,2,3,4-cyclobutanetetracarboxylic acid, 1,2,3,4-cyclopentanetetracarboxylic acid dianhydride, 2,3,5-tricarboxycylcopentylacetic acid dianhydride, 3,5,6-tricarboxynorbonane-2-acetic acid dianhydride, 2,3,4,5-tetrahydrofurantetracarboxylic acid dianhydride, 5-(2,5-dioxotetrahydrofural)-3-methyl-3-cyclohexene-1,2-dicarboxylic acid dianhydride, bicyclo[2,2,2]-oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride); aromatic tetracarboxylic acid dianhydrides (for example, pyromellitic acid dianhydride, 3,3xe2x80x2,4,4xe2x80x2-benzophenonetetracarboxylic acid dianhydride, 3,3xe2x80x2,4,4xe2x80x2-biphenylsulfonetetracarboxylic acid dianhydride, 1,4,5,8-naphthalenetetracarboxylic acid dianhydride, 2,3,6,7-naphthalenetetracarboxylic acid dianhydride, 3,3xe2x80x2,4,4xe2x80x2-biphenyl ether tetracarboxylic acid dianhydride, 3,3xe2x80x2,4,4xe2x80x2-dimethyldiphenylsilanetetracarboxylic acid dianhydride, 3,3xe2x80x2,4,4xe2x80x2-tetraphenylsilanetetracarboxylic acid dianhydride, 1,2,3,4-furantetracarboxylic acid dianhydride, 4,4xe2x80x2-bis(3,4-dicarboxyphenoxy)diphenylsulfide dianhydride, 4,4xe2x80x2-bis(3,4-dicarboxyphenoxy)diphenylsulfone dianhydride, 4,4xe2x80x2-bis (3,4-dicarbophenoxy) diphenylpropane dianhydride, 3,3xe2x80x2,4,4xe2x80x2-perfluoroisopropylidenediphthalic acid dianhydride, 3,3xe2x80x2,4,4xe2x80x2-biphenyltetracarboxylic acid dianhydride, bis(phthalic acid) phenylphosphine oxide dianhydride, p-pheneylene-bis(triphenylphthalic acid) dianhydride, m-phenylene-bis(triphenylphthalic acid) dianhydride, bis (triphenylphthalic acid)-4,4xe2x80x2-diphenyl ether dianhydride, bis(triphenylphthalic acid)-4,4xe2x80x2-diphenylmethane dianhydride); 1,3,3a,4,5,6,9b-hexahydro-2,5-dioxo-3-furanyl)-naphth[1,2-c]furan-1,3-dione, 1,3,3a,4,5,9b-hexahydro-5-methyl-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphth[1,2-c]furan-1,3-dione and 1,3,3a,4,5,9b-hexahydro-8-methyl-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphth[1,2-c]furan-1,3-dione.
Further examples of the acid dianhydrides usable herein include aliphatic tetracarboxylic acid dianhydrides having aromatic rings, for example, compounds represented by the following general formula (3): 
wherein Ra represents a divalent organic group having an aromatic ring; and Rb and Rc represent each a hydrogen atom or an alkyl group;
and compounds represented by the following general formula (4): 
wherein Ra, Rb and Rc are each as defined above.
These acid dianhydrides may be used either alone or as a combination of two or more thereof.
As the diamine to be used in the polyimide, various diamines are usable in addition to diamines having a cinnamic acid skeleton. Arbitrary diamines may be used without restriction. Examples thereof include aromatic diamines (for example, p-phenylenediamine, m-phenylenediamine, 4,4xe2x80x2-diaminodiphenylmethane, 4,4-diaminophenylethane, 4,4xe2x80x2-diaminophenyl ether, 4,4xe2x80x2-didiaminophenyl sulfide, 4,4xe2x80x2-didiaminophenyl sulfone, 1,5-diaminonaphthalene, 3,3-dimethyl-4,4xe2x80x2-diaminobiphenyl, 5-amino-1-(4xe2x80x2-aminophenyl)-1,3,3-trimethylindan, 6-amino-1-(4xe2x80x2-aminophenyl) 1,3,3-trimethylindan, 4,4xe2x80x2-diaminobenzanilide, 3,5-diamino-3xe2x80x2-trifluoromethylbenzanilide, 3,5-diamino-4xe2x80x2-trifluoromethylbenzanilide, 3,4xe2x80x2-diaminodiphenyl ether, 2,7-diaminofluorene, 2,2-bis(4-aminophenyl)hexafluoropropane, 4,4xe2x80x2-methylene-bis(2-chloroaniline), 2,2xe2x80x25,5xe2x80x2-tetrachloro-4,4xe2x80x2-diaminobiphenyl, 2,2xe2x80x2-dichloro-4,4xe2x80x2-diamino-5,5xe2x80x2-dimethoxybiphenyl, 3,3xe2x80x2-dimethoxy-4,4xe2x80x2-diaminobiphenyl, 4,4xe2x80x2-diamino-2,2xe2x80x2-bis(trifluoromethyl)biphenyl, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, 1,4-bis(4-aminophenoxy)benzene, 4,4xe2x80x2-bis (4-aminophenoxy)-biphenyl, 1,3xe2x80x2-bis(4-aminophenoxy)benzene, 9,9-bis(4-aminophenyl)fluorene, 4,4xe2x80x2-(p-phenyleneisopropylidene)bisaniline, 4,4xe2x80x2-(m-phenyleneisopropylidene)bisaniline, 2,2xe2x80x2-bis [4-(4-amino-2-trifluoromethylphenoxy)phenyl]hexafluoropropane, 4,4xe2x80x2-bis[4-(4-amino-2-trifluoromethyl)phenoxy]-octafluorobiphenyl); aromatic diamines having two amino groups bonded to an aromatic ring and hetero atom(s) other than the nitrogen atoms in these amino groups (for example, diaminotetraphenylthiophene); and aliphatic diamines and alicyclic diamines (for example, 1,1-metaxylylenediamine, 1,3-propanediamine, tetramethylenediamine, pentamethylenediamine, octamethylenediamine, nonamethylenediamine, 4,4-diaminoheptamethylenediamine, 1,4-diaminocycloheaxne, isophoronediamine, tetrahydrodicyclopentadienylenediamine, hexahydro-4,7-methanoindanylenedimethylenediamine, tricyclo[6,2,1,02.7]-undecylenedimethyldiamine, 4,4xe2x80x2-methylenebis (cyclohexylamine)).
Further examples of the diamine usable herein include, for example, mono-substituted phenylenediamines represented by the following general formula (5): 
wherein Rd represents a divalent organic group selected from among xe2x80x94Oxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94CONHxe2x80x94 and xe2x80x94COxe2x80x94; and Re represents a monovalent organic group having a steroid skeleton;
and compounds represented by the following general formula: 
wherein Rf represents a C1-12 hydrocarbon group; y is an integer of from 1 to 3; and z is an integer of from 1 to 20.
Further examples of the diamine include diamines having a photosensitive group, for example, 2xe2x80x2-(3,5-diaminobenzoate)-chalcone, 7xe2x80x2-(3,5-diaminobenzoate)-coumarin, (3,5-diaminobenzoate)-cinnamic acid, coumarin-3-carboxylate-(3,5-diaminophenyl), coumarin-3-carboxylate-1-(3,5-diaminophenyl ester), 1-(3,5-diaminophenoxy)-2-(cumarin-3-carboxylate)ethane, 1-(3,5-diaminophenoxy)-2-(xcex1-pyrone-5-carboxylate)ethane, 3-(3,5-diaminobenzoate)-propionate-(2-chalcone), 1-(3,5-diaminobenzoate)-2-(coumarin-3-carboxylate)ethane, 1-(3,5-diaminophenyl)-coumarin-3-carboxamide, 3,5-diaminobenzyl cinnamate, 3,5-diaminophenyl cinnamate, 2-(2,4-diaminophenoxy)ethyl-1-cinnamate, 2-(2,4-diaminophenoxy)ethyl-1-cinnamate, 2-(3,5-diaminobenzoic acid)propyl-1-cinnamate, (4xe2x80x2-aminophenyl)-4-aminocinnamate, (3-aminophenyl)-3-aminocinnamate, 1xe2x80x2-amino-2xe2x80x2-naphthyl-(3-aminocinnamate), 1,3-bis(4-aminocinnamic acid)benzene and 1,2-bis(4-aminocinnaic acid)ethyl. Either one of these diamine compounds or a combination of two or more thereof may be used.
Next, the process 2) wherein 1 equivalent of an arbitrary diamine is reacted with 2 equivalents of trimellitic acid anhydride chloride or with 2 equivalents of trimellitic acid anhydride in the presence of a condensing agent to give a dicarboxylic acid which is then reacted with a diamine having an alkyl or fluoroalkyl group thereby giving a polyimide will be illustrated as another example of the process for producing the polyimide according to the invention.
An arbitrary diamine (H2Nxe2x80x94Yxe2x80x94NH2) is reacted with trimellitic acid anhydride and subjected to cyclodehydration to give a dicarboxylic acid represented by the following general formula: 
wherein Y represents a divalent organic group.
Next, this dicarboxylic acid is reacted with a diol or a diamine represented by one of the following general formulae: 
wherein Z represents xe2x80x94CH2CH(COOR2)CH(COOR2)CH2xe2x80x94, xe2x80x94CH2CH(OCOR2)CH(OCOR2)CH2xe2x80x94, xe2x80x94CH2C(CH2COOR2)2CH2xe2x80x94, xe2x80x94CH2C(CH2OCOR2)2CH2xe2x80x94, xe2x80x94CH(CH2COOR2)CH(CH2COOR2)xe2x80x94 or xe2x80x94CH(CH2COOR2)CH(CH2OCOR2)xe2x80x94;
in the presence of a condensing agent to thereby give the desired polyimide having an alkyl or fluoroalkyl group.
The process for producing the polyimide according to the invention is not restricted to the processes as described above. A polyimide having an alkyl or fluoroalkyl group can be obtained by reacting 1 equivalent of diamines having an alkyl or fluoroalkyl group employed in the synthesis of the acid dianhydrides of general formulas (2-5), (2-6) and (2-7) (or a mixture of these diamines with other arbitrary diamines) with 1 equivalent of trimellitic acid anhydride chloride or with 1 equivalent of trimellitic acid anhydride in the presence of a condensing agent.
The polyimides according to the invention thus obtained may be mixed with various organic additives or inorganic fillers or various reinforcing agents to thereby provide compositions containing the polyimides.
One of the characteristics of the novel polyimides of the invention obtained by the above processes resides in having a low water absorption, which makes these polyimides appropriate for various uses.
The water absorption of the polyimides of the invention, measured in accordance with ASTM D570 under the conditions as employed in Example 1, is typically 1.8% or less, preferably 1.5% or less.
Now, the invention will be described in greater detail by reference to the following Examples. However, it is to be understood that the invention is not construed as being limited thereto.
In the following Examples, ESDA means 2,2-bis(4-hydroxyphenyl)propanedibenzoate-3,3xe2x80x2,4,4xe2x80x2-tetracarboxylic acid dianhydride; 6FDA means 2,2xe2x80x2-hexafluoropropylidenediphthalic acid dianhydride; BAPS-M means bis[4-(3-aminophenoxy)phenyl]sulfone; DMAc means N,N-dimethylacetamide; and DMF means N,N-dimethylformamide.
Weight-average molecular weight was measured by using GPC (manufactured by Waters) under the following conditions: columns (2): KD-806M manufactured by Shodex, 60xc2x0 C., detector: RI, flow rate: 1 ml/min, developing solvent: DMF (lithium bromide 0.03M, phosphoric acid 0.03 M), sample concentration: 0.2wt %, injection: 20 xcexcl, standard: polyethylene oxide.
Water absorption was measured in accordance with ASTM D570.